ChaumPedersenProof.java

package com.rau.evoting.ElGamal;

import java.io.Serializable;
import java.math.BigInteger;

import com.rau.evoting.utils.Pair;
import com.rau.evoting.utils.RandomHelper;

public class ChaumPedersenProof implements Serializable{

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	private BigInteger y1;
	private BigInteger y2;
	private BigInteger a1;
	private BigInteger a2;
	private BigInteger k;
	private BigInteger c;
	private BigInteger s;
	private BigInteger r;

	private BigInteger g;
	private BigInteger p;
	private BigInteger y;

	private BigInteger res1;
	private BigInteger res2;

	
	public ChaumPedersen generate(BigInteger pubKey, BigInteger r) {
		g = GlobalParameters.getParams().getG();
		p = GlobalParameters.getParams().getP();
		y = pubKey;
		this.r = r;

		y1 = g.modPow(r, p);
		y2 = y.modPow(r, p);
		System.out.println("y1:" + y1);
		System.out.println("y2:" + y2);
		
		ProverIteration1();
		VerifierIteration1();
		ProverIteration2();
		VerifierIteration2(); 

		System.out.println("p:" + p);
		System.out.println("s:" + s);
		System.out.println("k:" + k);
		
		System.out.println("a1:" + a1);
		System.out.println("a2:" + a2);
		System.out.println("res1:" + res1);
		System.out.println("res2:" + res2);
		
		ChaumPedersen cp = new ChaumPedersen(null, null, y, null, null, null, a1, a2, s);
		return cp;
	}

	public Pair<BigInteger, BigInteger> ProverIteration1() {
		k = RandomHelper.randomNonZeroBigInteger(p
				.subtract(new BigInteger("1")));
		//k = 2;
		a1 = g.modPow(k, p);
		a2 = y.modPow(k, p);
		return new Pair<BigInteger, BigInteger>(a1, a2);

	}

	public BigInteger ProverIteration2() {
		BigInteger temp = c.multiply(r);//.mod(p);
		s = (k.subtract(temp)) ;//.mod(p);
		return s;
	}

	public BigInteger VerifierIteration1() {
		String temp = a1.toString().concat(a2.toString());
		long t2 = temp.hashCode();
		c = BigInteger.valueOf(t2).mod(p);
		//c = new BigInteger("111");
		// RandomHelper.randomNonZeroBigInteger(pubKey.getParameters().getP()
		// .subtract(new BigInteger("1")));
		return c;
	}

	public boolean VerifierIteration2() {
		res1 = g.modPow(s, p).multiply(y1.modPow(c, p)).mod(p);
		res2 = y.modPow(s, p).multiply(y2.modPow(c, p)).mod(p);

		if (a1.equals(res1) && a2.equals(res2))
			return true;

		return false;
	}

	public BigInteger getA1() {
		return a1;
	}

	public BigInteger getA2() {
		return a2;
	}

}